Variable orifice plate for coal pipes

ABSTRACT

A flow control apparatus for a coal pipe containing a stream of primary combustion air carrying pulverized solid fuel particles, includes a frame sealingly secured to an outside surface of the coal pipe around a window opening formed on one side of the pipe. An orifice plate having an orifice opening at the center is supported for pivotal movement in the coal pipe on a spindle extending radially outwardly from an edge portion on one side of the orifice plate and out through the window opening in the pipe. A bearing sleeve is provided for supporting the spindle for rotating movement about a spindle axis extending transversely of the coal pipe across the center thereof. A mounting plate structure for the sleeve is provided and is attached to the frame. A removable handle is attached on an outer end of the spindle for rotating the orifice plate in the coal pipe to vary the effective flow cross-section of the orifice opening for controlling the flow of coal and primary air to a burner.

This application is a division of application Ser. No. 08/599,169 filedNov. 13, 1995 now U.S. Pat. No. 5,593,131.

BACKGROUND OF THE INVENTION

1. FieId of the Invention

The present invention relates to a new and improved variable orificeplate for controlling the flow in coal pipes supplying burners infurnaces and boilers. More particularly, the present invention isdirected to an orifice plate mounted in a coal pipe and movable betweenalternate positions to vary the effective flow cross-section forcontrolling the flow of primary coal and air to a burner. By adjustingthe angle of tilt of the orifice plate relative to the general directionof flow along a coal pipe, the effective flow cross-section through theorifice opening is varied and adjustments can be made while on-lineduring operation of a burner so that the effects of position settingsare rapidly available and easily tabulated without requiring the burnerto be shut down.

2. Background of the Prior Art

There has been an historical problem of obtaining balanced pulverizedcoal flow in multiple coal pipe distribution systems. Typically, coalpipes are manifolded from the discharge of a pulverizer. A manifold canbe in the form of a classifier, a flow splitter or a riffle box.Previously, a method used to equalize coal flow to each burner was tothrottle each coal line to obtain equal pressure drops through all ofthe multiple coal lines. Because of the nature of two phase flow,including solid pulverizer coal and primary air, several iterations ofthrottling action were often required to obtain even a temporary coalline balance of plus or minus 10% of the average flow rate in each pipe.Because of the increased need to maintain good coal flow with low NO_(X)firing, typical previous trial and error methods have not worked.

A new and improved variable orifice plate for coal pipes in accordancewith the present invention is useful in a wide variety of pulverizedcoal supply systems having multiple coal pipes and is especially welladapted for use in systems for supplying multiple burners of all typesof furnaces including "TURBO" furnaces such as that shown and describedin U.S. Pat. No. 4,517,904, incorporated herein by reference and sold bythe assignee herein under the trademark "TURBO" _(R).

U.S. Pat. No. 1,477,824 discloses a powdered material firing apparatusemploying cylindrically-shaped air valve positioned upstream from thepoint of coal introduction into the stream.

U.S. Pat. No. 1,708,496 discloses a pulverized fuel burner employingrotatably mounted solid circular damper disks in separate fuel and airconduits connected to supply the burner.

U.S. Pat. No. 2,079,420 discloses a burner for firing furnaces withpulverized coal wherein a pair of semi-circular-shaped valves areprovided at the inlet end of the burner for dividing the flow betweenseparate nozzle sections.

U.S. Pat. No. 3,002,472 discloses a comminution system for wet solidmaterials (coal) including generally circular dampers in coal and airpipes feeding a steam generating unit.

U.S. Pat. No. 4,459,922 discloses an externally adjustable pipe orificeassembly employing pivoted plates.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a new and improvedvariable orifice plate for use in a coal pipe connected to supply fuelburning apparatus and more particularly, to provide a new and improvedmultiple pipe coal supply system for a furnace provided with pluralstreams of coal and primary air having variable orifice plates inaccordance with the present invention installed therein for providingon-line balancing of coal flow to multiple burners.

Yet another object of the present invention is to provide a new andimproved coal supply system for an existing or new multiple burnerfurnace which includes a new and improved orifice plate in each coalpipe for on-line adjusting and balancing coal flow to respectiveburners.

Still another object of the present invention is to provide a new andimproved coal supply system of the character described having pressuretaps before and after each orifice plate to measure changes in pressuredrop.

Another object of the present invention is to provide a new and improvedcoal pipe orifice plate apparatus which does not require dismantling ofexisting coal piping for installation.

Still another object of the present invention is to provide a new andimproved coal pipe orifice plate which is readily adjustable tocompensate for wear and abrasion, which requires no special tools tooperate, which has a removable handle to prevent unintended operation,which has a pressure-tight leak proof seal, which does not tend toaccumulate a build up of pulverized coal and which may be constructed ofheat and wear resistant material.

Yet another object of the present invention is to provide a new andimproved coal pipe orifice plate which can be installed in a neutralposition parallel to the flow axis of a coal pipe with a zero pressuredrop before testing and set up is commenced to provide a fail safestarting condition.

Still another object of the present invention is to provide a new andimproved coal pipe orifice plate which is supported from one side of acoal pipe rather than from two opposite sides and which may bepositively locked in a selected position chosen from a plurality ofdifferent positions available.

Another object of the present invention is to provide a new and improvedcoal pipe orifice plate that can be used in conjunction with all typesof coal pulverizers.

BRIEF SUMMARY OF THE PRESENT INVENTION

The foregoing and other objects and advantages of the present inventionare accomplished in a new and improved flow control apparatus for a coalpipe containing a stream of primary combustion air carrying pulverizedsolid fuel particles, including a frame sealingly secured to an outsidesurface of the coal pipe around a window opening formed on one side ofthe pipe. A circular, single piece, annular orifice plate having anorifice opening at the center is supported for pivotal movement in thecoal pipe on a spindle extending radially outwardly from an edge on oneside of the orifice plate and out through the window opening.

A bearing sleeve for supporting the spindle for rotating movement abouta spindle axis extending transversely of the coal pipe across the centeris carried on a mounting plate which closes off the frame.

A removable handle is mounted on an outer end of the spindle forrotating the orifice plate in the coal pipe to vary the effective flowcross-section of the orifice opening to control the flow of coal andprimary combustion air.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference should behad to the following detailed description taken in conjunction with thedrawings, in which:

FIG. 1 is a sectional and elevational view of a furnace and fuel supplysystem in accordance with the features of the present invention;

FIG. 2 is an enlarged, fragmentary, elevational view of a coal pipe witha variable orifice plate in accordance with the present inventioninstalled therein of the furnace;

FIG. 3 is a fragmentary, longitudinal cross-sectional view takensubstantially along lines 3--3 of FIG. 2; and

FIG. 4 is a fragmentary, transverse cross-sectional view takensubstantially along lines 4--4 of FIG. 2.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring now more particularly to the drawings, in FIG. 1 isillustrated a new and improved furnace and fuel supply systemconstructed in accordance with the features of the present invention andreferred to generally by the reference number 10.

The furnace and fuel supply system 10 includes an upstanding furnace 12for burning pulverized coal or other fossil fuels, which fuels may besupplied from a storage system including a hopper 14 in a case when coalis used as fuel, or in tanks, pipelines, etc. (not shown) in cases whenother fossil fuels are used.

Coal from the hopper 14 flows down through an outlet in communicationwith an inlet or feed chute 16 of a drum type coal feeder 18. The feeder18 is driven by a variable speed drive unit 20 to provide an appropriatefuel feeding rate as controlled by an automatic fuel feed control 22which is set to respond to the furnace demand for fuel.

Coal from the drum type feeder 18 flows down an outlet chute 24 througha vertical coal feed chute 25 to the inlet side of a coal pulverizer 28in which the lumps of coal are broken down to a fine powder or dust forburning in the furnace 12. Primary combustion air for the furnace 12 issupplied through a windbox 30 on side walls 32 of the furnace 12. A fanor blower 26 directs primary air and coal into the pulverizer 28.Secondary air supplied from the windbox 30 enters the interior of thefurnace 12 through openings 44 in side wall sections 46 of the furnaceopening immediately surrounding coal nozzles 60 which supply fuel forthe furnace.

A secondary air supply duct system 34 provides secondary air to thewindbox 30 and includes a fan or blower 35 having an outlet connected toa duct 37 feeding the windbox. Primary combustion air is taken from thewindbox 30 through a shut-off damper valve 40 and is directed into thecoal feed chute via branch ducts 38 and 39. Below the windbox 30, thefurnace 12 includes inwardly and downwardly sloping wall sections 48adjacent a lower end 50 of a turbulent combustion chamber 42.

The primary air flow in the duct 38 from the windbox 30 is modulated bya suction control damper 52 which is driven and controlled by a suctioncontroller 54 having a sensor downstream of the damper. The air flow inthe duct 39 is modulated by an air temperature damper 56 driven andcontrolled by a air temperature controller 58 having a sensor on thedischarge or outlet side of the coal pulverizer 28. An alarm 57 of avisual or audible type and a temperature indicator 59 are associatedwith the air temperature controller 58 and the sensor circuit connectedto the outlet side of the coal pulverizer 28.

In accordance with the present invention, the furnace 12 is providedwith one or more, new and improved, burner coal nozzles 60 constructedin accordance with the features of the present invention. Each burnercoal nozzle 60 is centrally disposed in a burner opening 44 in thecombustion chamber wall section 46 and includes a main duct or conduitsection 62 having a flanged inlet 64 at an outer end secured to anoutside wall 66 of the windbox 30 around a circular opening 68 providedtherein in coaxial alignment with an associated burner opening 44 in thecombustion chamber wall section 46. The inlet flange 64 of the burnercoal nozzle 60 is connected to a flanged elbow 70, which in turn isconnected to a coal/air pipe 72 for supplying a controlled flow ofprimary combustion air and pulverized coal to the burner.

Each coal pipe 72 is supplied with primary combustion air which carriesthe pulverized coal from an outlet duct or section 74 of the coal millor pulverizer 26. The outlet duct 74 is connected to a transitionsection 76 having plural outlets, each of which is connected to anair/coal control damper 78 for modulating the flow of primary combustionair and pulverized coal carried thereby to the burner coal nozzle 60 viaa coal pipe 72. The air/coal control dampers 78 are controlled andinterconnected with the automatic fuel feed controller 22 which controlsthe drum type coal feeder 18 as previously described.

Upstream of the air/coal dampers 78 each coal pipe 72 is provided with avariable orifice control plate apparatus 80, adjustable to vary theeffective cross-sectional flow area through each pipe to more preciselybalance and control the amount of primary air and pulverized coalsupplied to each burner coal nozzle 60 of the furnace 12. Upstream ofthe variable orifice control plate apparatus 80, each coal pipe 72 isprovided with a shut-off valve 82 for cutting off the supply of primarycombustion air and pulverized coal to the furnace 12.

Referring now more particularly to FIGS. 2, 3 and 4, the variableorifice plate control apparatus 80 is adapted to be rapidly installed onexisting coal pipes 72 without requiring the dismantling thereof and, ofcourse, is readily installed in new coal piping systems. The apparatusincludes a rectangular frame 84 made up of upper and lower angle members86 and 88, joined at upper and lower ends to opposite side frame anglemembers 90. The frame 84 is mounted on one side of the coal pipe 72 tosurround the edges of a rectangular-shaped window 72a cut from the wallof the coal pipe, usually with a cutting torch or saw.

The angle frame members have flanges 86a, 88a and 90a joined to the wallof the coal pipe 72 by welding 92 extending around the window 72aproviding a gas tight seal. The angle frame members include face flanges86b, 88b and 90b at right angles to the flanges 86a, 88b and 90b,respectively, which lie in a common plane spaced outwardly of the coalpipe 72 generally parallel of a longitudinally extending, central flowaxis 94. The longitudinal flow axis 94 is intersected at the center ofthe coal pipe 72 by a radially outwardly extending transverse spindleaxis 96 at right angles thereto which is positioned at the center of therectangular frame 84 as best shown in FIGS. 3 and 4.

In accordance with the present invention, an annular orifice plate 98formed of heat and abrasion resistant metal plate is supported in thecoal pipe 72 for pivotal movement about the spindle axis 96 betweenselected different angular positions relative to the coal pipe flow axis94 for controlling the flow of primary combustion air and coal flowingin the coal pipe.

The annular orifice plate 98 has a circular outer peripheral edge with adiameter slightly less than the inside diameter of the coal pipe 72 asbest shown in FIG. 4. The orifice plate 98 is formed with a smallerdiameter orifice opening 100 at the center through which a flowingstream of primary air and coal in the coal pipe 72 passes. Because theouter diameter of the orifice plate 98 is less than the inside diameterof the coal pipe 72, some of the primary air and coal stream will flowaround the outer periphery of the orifice plate adjacent the inside wallsurface of the coal pipe even when the orifice plate is positioned atright angles to the flow axis 94.

The orifice plate 98 is supported from a side edge portion thereof by aspindle 102 having an inner end joined to a radially slotted out edgeportion of the orifice plate. The spindle 102 is supported for rotationabout the axis 96 in a bearing sleeve 104 extending inwardly toward thewindow opening 72a of the coal pipe from an apertured, rectangular,mounting plate 106 secured to the flanges 86b, 88b and 90b by aplurality of bolt and nut assemblies 108. The mounting plate 106 and thebearing sleeve 104 which is welded thereto are removable by loosening upthe bolt and nut assemblies 108 and accordingly, the orifice plate 98can be easily removed for inspection, repair and replacement whennecessary.

A space 110 (FIG. 3) between the window opening 72a and the mountingplate 106 may be filled with a box-like channel-shaped filler element112 which is secured to the mounting plate by welding as best shown inFIG. 3. These intermediate level nut and bolt assemblies 108 are alsoused to attach an apertured, square-shaped outer stiffening plate 114 atthe center of the mounting plate 106. An O-ring seal 116 is provided onthe spindle 102 between the mounting plate 106 and the facing insidesurface of the stiffening plate 114 to provide a gas tight seal. Thestiffening plate 114 is provided with a threaded positioning aperture114a (FIG. 3) offset radially outwardly from a central spindle aperture.The positioning aperture 114a is designed to receive a position securingcap screw 118 for securing the orifice plate 98 and spindle 102 in aselected angular position relative to the flow axis 94 of the coal pipe72.

An outer end portion of the spindle 102 is supported in an outer sleeve120 which is mounted on a positioning plate 122 having a centralaperture for the spindle, and a plurality of position setting apertures122a, 122b, 122c, etc., spaced radially outwardly of the spindle atdifferent angles representing different angular positions of the orificeplate 98 relative to the flow axis 94 of the coal pipe 72. A handle 124extends through the outer sleeve 120 and an aperture in the outer endportion of the spindle 102 for rotating the orifice plate 98 and thepositioning plate 122 to a selected angular position in the coal pipe 72wherein a particular aperture 122a, 122b, 122c on the plate 122 isaligned with the threaded positioning aperture 114a on the stiffeningplate 114. The handle 124 may be removed by withdrawing the handlelongitudinally from the outer sleeve 120 and the spindle 102 to preventunwanted, unintended position changing after a position is selected andthe locking cap screw 118 is secured in place.

It will thus be seen that the angular position of the orifice plate 98relative to the flow axis 94 of the coal pipe 72 is adjustable andlockable in selected positions to provide the desired throttling actionon the stream of flowing primary combustion air and coal in the coalpipe. By changing the angular position, the effective flow cross-sectionin the coal pipe 72 around the outer edges of the orifice plate 98 andthrough the central orifice opening 100 is changed to provide balancedfuel flow to each of the burners 60 in the furnace 12. When the orificeplate 98 is positioned at right angles to the flow axis 94 (solidlines--FIGS. 2, 3 and 4) a maximum throttling action is obtained and theamount of pressure drop can be measured instantly after a change is madeby means of manometers 126 and 128 upstream and downstream of theorifice plate.

Adjustment and changes of the angle of the orifice plate 98 in the coalpipe 72 can be accomplished on-line while the furnace 12 is in operationand results of the changes are known immediately so that orifice plates98 for each burner 60 can be individually tuned to provide the mostefficient furnace operation. It should also be noted that on an initialoperational start up after installation of an orifice plate apparatus84, the orifice plate 98 can be positioned in an in-line or neutralstate, parallel to flow axis 94 (zero pressure drop) before testing andsetup begin to provide a fail safe starting point.

Installation of the orifice plate assemblies 84 in existing coal pipes72 is made simpler because the orifice plates 98 are supported incantilever arrangement on the spindles 102 from one rather than bothsides of the coal pipe. Only a single window opening 72a on one side ofa coal pipe 72 need be made and dismantling of the coal pipe is notrequired as with other types of two point support axle systems.Moreover, the unique frame 84 and mounting plate 106 in combinationpermit rapid access to the orifice plate 98 and spindle 102 forservicing, removal and replacement when necessary.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. Thus, it is to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described above.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. In combination, a furnace including a plurality ofburners, one or more pulverizers for comminuting solid fuel into smallparticles for transport with primary combustion air, a plurality of coalpipes interconnected between said pulverizer(s) and an associated burnerfor transporting a stream of pulverized solid fuel and primarycombustion air to said furnace; anda flow controlling orifice platepivotally mounted in each coal pipe and movable between selectedpositions therein for equalizing adjustment and balancing of fuelsupplied to all of said burners during operation of said furnace, andmeans for measuring static pressure upstream and downstream of theorifice plate in each coal pipe for determining a selected position forthe orifice plate.
 2. The combination of claim 1, wherein:the orificeplate in each coal pipe is pivotal between a position aligned with theaxis of the pipe and a position transverse therein.
 3. The combinationof claim 2, including:lock means for each orifice plate for securing theplate in a selected angular position relative to the axis of a coal pipein which the plate is mounted.